1. Field of the Invention
The present invention relates to a steam-iron sole-plate formed by assembling together a plurality of metal sheets brazed to each other, a flat resistance-type heating element being placed between two of said sheets.
2. Description of the Prior Art
Laundry irons which are currently available on the market have a heating resistor which is insulated from the frame ground of the appliance by an insulating layer designated by NF standards as a "principal functional insulator". This insulator can be a coating of magnesia in the case of a screened resistor, a sheet of micanite in the case of a clamped flat heating element, etc. Accordingly, the power supply cord must have a ground lead in addition to the current supply leads. These appliances are designated as Class I. The three leads just mentioned require a cord of large diameter and, if it is desired to use a cord winder, this storage device will have to be bulky, thus resulting in excessive costs.
European as well as American and Japanese standardization allows suppression of the ground lead if insulation of the resistor with respect to the ground of the appliance is achieved by an insulating layer of 1 mm, or by two superposed and separable insulating layers in addition to the principal insulation, namely three layers on each side of the heating element. These appliances are in this case designated as Class II. The power supply cord need have only two lead wires, thus making it possible to mount cord winders of small overall size.
The aim of the present invention is to produce a sole-plate for a steam or dry iron of Class II at a highly competitive cost price without any modification of the thermal properties of the iron. In fact, since the presence of an insulator having a thickness of 1 mm on each side of the heating element has the effect of considerably braking the transmission of heat, it is possible to employ sheets of micanite having a thickness of 0.1 mm, the electrical rigidity of which conforms to the prescribed standard (2500 volts). By virtue of their small thickness, these sheets of micanite have the property of being transparent to infrared radiation. Moreover, although the prescribed standard makes it necessary to double the number of insulators between the functional insulator and ground, the resulting thickness of 0.2 mm constitutes only a negligible brake for transmission of heat by conduction.
It should be noted that the total thickness of the heating element and of the four insulating sheets is 1 mm.+-.0.1, namely 0.5 mm.+-.0.05 between the heating element and the mass of metal to be heated.
The present Applicant has described in his French patent Application No. 88 02625 filed on Mar. 2nd, 1988 a flat heating component comprising a resistance-type heating element embedded in electrically insulating material and placed between two metal plates secured to each other by means of a series of welded joints made through gaps formed in the heating element. These welded joints are made by brazing which is obtained by melting a sheet of brazing alloy roll-bonded with either or both of the two metal plates.